1. Field of the Invention
The present invention relates to a semiconductor device and a manufacturing method of a semiconductor device. Note that in this specification, a semiconductor device refers to devices in general that function by utilizing a semiconductor characteristic.
2. Description of the Related Art
In recent years, manufacturing of semiconductor devices that utilize thin film transistors as switching elements, in which the thin film transistors (hereinafter also referred to as a “TFT”) are formed over substrates having insulating surfaces, such as glass, has been actively pursued. In the thin film transistor, an island-shaped semiconductor layer is formed over a substrate that has an insulating surface, and a portion of the island-shaped semiconductor layer is used as a channel-forming region of the transistor.    Patent Document 1: Japanese Published Patent Application No. H8-335702    Patent Document 1: Japanese Published Patent Application No. H3-22567